<!DOCTYPE html>
<html lang="cn">
<head>
    <meta charset="UTF-8">
    <title>状态伪类</title>
    <style>
        td {
            border: 2px solid black;
            text-align: center;
        }
        
        td:empty::after{
           content: "/"; 
        }
    </style>
</head>
<body>
<table style="width: 200px;height: 300px;border-collapse: collapse;">
    <tr>
        <td>姓名</td>
        <td>二级</td>
        <td>四级</td>
    </tr>
    <tr>
        <td>张三</td>
        <td>61</td>
        <td></td>
    </tr>
    <tr>
        <td>李四</td>
        <td></td>
        <td>620</td>
    </tr>
    <tr>
        <td>王五</td>
        <td></td>
        <td></td>
    </tr>
</table>
</body>
</html>